This paper describes development of an electric current sensor for measuring a large current. A magnetic saturatable detector is used in place of a Hall detector in the conventional current sensor. The sensor is developed with low price and high stability for parameter deviations caused on a temperature variation and such a disturbance. The balanced large current driving circuit which excites a magnetic detector with very low offset voltage and some techniques are proposed as new circuits which detect the inductance changes caused on a magnetic flux. These sensing circuits realize a stable step for a large current.